Technical Field
The present disclosure relates to a MEMS (MicroElectroMechanical System) sensor device with reduced stress-sensitivity, and to a corresponding manufacturing process.
Description of the Related Art
In integrated semiconductor devices, and particularly in MEMS devices, mechanical stresses and strains occur, which may lead to undesired modifications and drifts of the electrical parameters, for example of the detection sensitivity.
MEMS devices typically include one or more dies of semiconductor material, in which the corresponding micromechanical detection structure and possibly a corresponding ASIC (Application-Specific Integrated Circuit) are provided, the latter for example including a corresponding interface for acquisition and pre-processing of the detected electrical quantities (for example, a capacitive variation indicating a detected pressure) for generation of an electrical output signal (which is supplied at the output from the MEMS device, for subsequent processing operations).
MEMS devices further include a package, which encloses and protects the dies of the detection structure and of the possible ASIC, further providing an interface for electrical connection with the outside world. In so-called “substrate-level package” solutions, the package is made by one or more base and cap layers, which are directly coupled to the dies of the MEMS device, constituting the interface thereof with the outside world.
It is known that mechanical stresses are induced in the dies housed within the package of the MEMS devices, typically due to deformations (for example, warping or other types of stress) of the same package, which are due for example to processes of soldering to an external printed-circuit board (PCB) and to the corresponding thermal stresses.
Given that the mechanical properties of the detection structures directly affect the performance of MEMS devices, a desire to reduce as far as possible the effects of the aforesaid stresses is evident.
A solution that has been proposed for reducing the effects of stresses and the resulting deformations is illustrated in FIGS. 1a and 1b, with reference, by way of example, to a MEMS device 1 that implements a pressure sensor.
MEMS device 1 comprises a supporting base 2, for example of silicon, having a bottom surface in contact with the outside world.
MEMS device 1 further comprises a sensor die 4, in which a micromechanical detection structure 5 (represented schematically) is made, for example for detecting pressure. The sensor die 4 is mechanically coupled to a sensor frame 6, which, as shown in the schematic top plan view of FIG. 1b, externally surrounds the sensor die 4, via elastic coupling elements 8, in the form of folded springs (for example, S-shaped in plan view).
The elastic coupling elements 8, in a way not shown, also carry electrical-connection paths, for electrical connection between the mechanical detection structure 5 and the sensor frame 6, which may integrate appropriate electrical elements and components, possibly an ASIC (not illustrated) coupled to the mechanical detection structure 5. The sensor frame 6 further carries contact pads 7 for electrical connection with the outside world, for example by electrical wires.
Via this mechanical coupling, the sensor die 4 is arranged suspended over the supporting base 2. Stoppers 9 are coupled to a bottom portion of the sensor die 4, being arranged between the same sensor die 4 and the supporting base 2, in order to limit the displacements undergone by the sensor die 4 in a vertical direction, due to elastic deformation of the elastic coupling elements 8.
MEMS device 1 further comprises a cap 10, arranged above the sensor die 4, coupled to a top surface of the sensor frame 6. An air gap is present between the sensor die 4 and the cap 10 so that the micromechanical detection structure 5 is free to move in detecting a relevant quantity (for example, a pressure).
In this solution, the presence of the elastic coupling elements 8 advantageously enables an elastic coupling between the sensor die 4 (and the corresponding micromechanical detection structure 5) and the sensor frame 6, so as to reduce stresses (for example, of a thermomechanical type) acting on the sensor die 4. In fact, possible deformations undergone by the sensor frame 6, for example due to soldering of the supporting base 2 to an external PCB, are at least in part “absorbed” by the elastic coupling elements 8 so that stresses transmitted to the sensor die 4 are reduced.